High-frequency coil with adjustable inductance value



Dec. 15, 1936. H. VOGT 2,064,772

HIGH FREQUENCY COIL WITH ADJUSTABLE INDUCTANCE VALUE Filed June 8, 1955 ift/5013.

a a/ @a 4Z 38 40 7 41 Y |ve 4Q/Z3 W I l :ssl jj Jrzr/venZ'a/'f 37 afz Volg?? Patented Dec. 15, 1936 UNITED STATES PATENT OFFICE HIGH-FREQUENCY COIL WITH ADJUSTABLE INDUCTANCE VALUE Application June 8, 1933, Serial No. 674,84

In Germany June 21, 1932 3 Claims.

This invention relates to high frequency tuning coils with magnet core and adjustable inductance value. The inductance value of tuning coils for radio receivers must be accurately matched and the margin of inductance especially in case of multistage sets must not exceed 1% of the total inductance. Inductance values of such accuracy are diiiicult to be produced.

The permeability of the magnetic material, the cross section of the magnetic cores etc. does not always turn out uniformly and, due to the much higher field intensity, also the influence of the number of turns, the spatial arrangement of the windings to the core and similar inferior influences are much more critical than in case of air coils. Such tuning coils therefore can be practically used only, if it is rendered possible to subsequently match the inductance value.

It is the object of this invention to render possible and to facilitate the accurate matching of iron cored radio coils, in particular of the type disclosed and claimed in my copending application Serial No. 674,847, filed June 8, 1933.

According to this invention the coils, preferably of the type disclosed together with a suitable iron powder core in my copending application Serial No. 674,847 iiled of even date with the present application, are accurately matched in such a way that the closed magnetic circuit is formed by two core parts which are separated from' one another by an air gap, the width of which is somewhat varied after the coil is iinished, until the desired inductance value is attained. The

core material used for radio coils is of very low permeability compared to the usual corematerials; therefore, the insertion of the air gap in this case has not the usual effect of severely reducing the inductance and necessitating the increase of the number of turns, but the inductance change due to the air gap is a very small one only,

just large enough to compensate for the small difference of the influence resulting in the manufacture.

The invention will be better understood by reference to the drawing, in which Fig. 1 shows a constructional arrangement to facilitate the air gap matching, in section.

Fig. 2 shows the same arrangement in side elevation.

Fig. 3 shows a ground plan of the same arrangement. Fig. 4 is an enlarged part-sketch of the coil illustrated in Figs. 1, 2, and 3 showing the fixing of the coil former on the core.

Fig. 5 is a section through an adjustable pot core construction for an adjustable coil.

Fig. 6 is stillv another form of adjustable coil construction in section, and

Fig. 7 a ground plan of the same coil.

A very .suitable arrangement to carry out the variationof the air gap and to fix it after adjustment is shown in Figs. 1, 2, and 3. The coil former I9 with the windings is movably arranged on the medium leg of the magnet core 20, which has the /shape of a shell core. Moreover the coil former is xed to the magnet bridge 2| (f. i. by pasting, dissolving of the coil former material or the like). The magnet bridge thus is guided on the magnet core and by means of moving the coil former to and fro on the magnet core it can be adjusted to the due distance. By this arrangement a careful adjustment is facilitated, the magnet parts being guided on each other in a very simple way, and securing of the final relative position of the magnet parts after adjustment is rendered possible as the coil former can be fixed to the magnet leg, f. i. by filling up the interstices with Wax like material Il, dissolving the material of the coil former with a suitable solvent or the like, as shown on larger scale in Fig. 4.

A coil with pot core is shown in Fig. 5. In this case the two core halves 22 and 23 are attached to each one of the two metal boxes Ma and Mb (f. i. by filling up the interstices with a filling mass Il) which are so combined that they can be adjusted relatively to each other in axial direction, preferably by a thread. An insulating layer of 1-2 mm. thickness should be arranged between the screen Ila and the core (22, 23): otherwise the damping of the coil would be considerably increased. By turning the boxes relatively to each other the width of the air gap l existing between the two magnet cores 22 and 23 can be adjusted at will. This arrangement offers the advantage that elastic means (rubber, bronze-springs or the like) which tend to cause instability and losses are avoided. The wire ends 5I may best be led out through that core half or box half, which is attached to the mounting plate 52 of the receiver by means of a screw 53. By putting a binding means, consisting of cement, solder orV the like, into a groove 54 arranged in the edge of the outer half of the screening cylinder Ma the system parts can be fixed relatively to each other after matching.

A construction according to the arrangement of Figs. 1-4 is shown in Figs. 6 and 7. There the magnet core 36 is suspended in an insulating piece 31 and xed in the screening cover 38 in such a way that its longitudinal extension is parallel to the central axis of the screening cover. The magnetic bridge 40 is held in a'second insulating piece 39, which by means of two springs 4| presses against the wall of the screening cover and can be caused to more or less approach the screening cover so that the air gap may be adjusted accordingly. Having adjusted the correct inductance value the coil former may be fixed to the magnet core as set forth above and the adjusting screw 42 may be covered by a little coverplate 43 or the like.

The constructions which render possible adjustment of the coil in screened condition, that is through the screen, are most suitable. The screening cover in this case at the same time may be used to suspend the adjusting means, as has been illustrated already in the several embodiments shown in Figs. 5, 6, and 7 above described. It is thus possible to match a plurality of coils in screened condition iitted in the receiver, so that any subsequent change after fitting due to the influence oi the screen or any metal parts or undesirable couplings in the receiver is avoided.

Due care has to be taken that the inductance value of the coil after adjustment remains constant independently of mechanical and heat inuences. Mechanical iniiuences are eliminated by making the suspension sufficiently rigid and by pasting up the system parts after adjustment or by iilling up the interstices (f. i. with a mixture of colophony and ceresin, the melting point of which is beyond or by providing tight threads in case that continuous adjustment by screws is provided, without positive fixing by iilling up or pasting up. Heat influences may be eliminated by compensating the occurring heat elongations (by providing suspension systems with suitable elongation coefiicients) and by using heat-proof pastes.

By the invention the construction of tuning coils with magnet core is rendered possible which in screened and tted condition can be accurately adjusted to an inductance value which remains constant after adjustment, thus facilitating the construction oi compact and accurately matched units.

I claim:-

1. A tuning coil for broadcast receivers comprising a screening cylinder, an E-shaped core, a bobbin arranged on the medium limb of said core, a magnetic bridge and means for varying the distance of said bridge from said core from the outside of the screening cover, said core being tightly fixed to the circumference of said screening cylinder with its longitudinal direction parallel to the central axis of said screening cylinder and said magnetic bridge being elastically suspended at the opposite side of said cover.

2. An inductance device for high frequency equipment comprising in combination a coil former of insulating-material, a multi-layer bobbin on said coil former, an E-shaped magnetic core part, the middle limb of which is movably guided in said coil former and a magnetic bridge, which is attached to said coil former and closes the magnetic core circuit formed by said E- shaped part, both of said core parts being composed of iron powder, insulating parts by which said core parts are suspended and mechanical means for varying the distance between said core parts.

3. An inductance device for high frequency equipment, comprising in combination a coil former of insulating material, a multi-layer bobbin on said coil former, a magnetic core composed of two component elements, at least one of which has an E-shaped section, the middle limb of which is surrounded by said coil former, the

other component element forming a magnetic bridge for the first-named component element to close the magnetic core circuits formed in said first-named element, both of said core elements being composed of iron powder, insulating parts by which said core elements are suspended, and mechanical means for varying the distance between saidcore parts.

HANS VOGT. 

